Fix to docker import issues and swagger error

This is actually two fixes in one change:
1. Fixing the import issues in the docker containers, also cleaning
   it up.
2. Avoiding the creation of multiple swagger.json files by specifying
   which of the proto files represent the top-level service.

Change-Id: I9fec5cf48df127725673ba53f0e91d2ed2e275ad
diff --git a/Dockerfile.voltha b/Dockerfile.voltha
index 405f499..f47f9c0 100644
--- a/Dockerfile.voltha
+++ b/Dockerfile.voltha
@@ -22,9 +22,11 @@
 MAINTAINER Nathan Knuth   <nathan.knuth@tibitcom.com>
 
 # Bundle app source
-COPY voltha /voltha
-COPY common /common
+RUN mkdir /voltha && touch /voltha/__init__.py
+ENV PYTHONPATH=/voltha
+COPY common /voltha/common
+COPY voltha /voltha/voltha
 
 # Exposing process and default entry point
 # EXPOSE 8000
-CMD ["python", "voltha/main.py"]
+CMD ["python", "voltha/voltha/main.py"]